Transmission of sound through the interface of phase-separated 3He-4He liquid mixtures : Kinetic growth coefficient of the interface

We report the results of the first systematic study of the dynamical properties of the interface between the phase-separated 3 He- 4 He liquid mixtures. With the acousic sound wave of 10MHz, we determined the kinetic growth coefficient of the interface in the temperature range from 150mK down to 7mK. Below about 70mK, it starts increasing with the decrease of temperature and shows an approximate temperature dependence of 1/T 2 . The magnitude and the temperature dependence cannot be explained with the existing theory of the hydrodynamic regime.